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CysR10 is essential for formation of the tightly compact, spherical shaped structure of PB-I.
Sulfur-rich prolamin gene CysR10 locates in chromosome 3, and encodes Cysteine-Rich 10 kDa Prolamin. RP10 , CysR10 , and crP10  represent the same gene. The rice prolamins consist of 60% Cys-rich prolamins and 40% Cys-poor prolamins, and the 10, 14 and 16 kDa prolamins are Cys-rich species, while the 13 kDa prolamin is a Cys-poor species . The 10 kDa prolamins (CysR10) share minimal sequence homology with the other two classes and are characterized by their high content of methionine (20%) and cysteine (10%) residues . In rice, there are two types of protein bodies (PBs), called PB-I in which prolamins are accumulated as intracisternal protein granules and PB-II. These prolamin species are asymmetrically distributed within PB-I and that CysR10 is essential for formation of the tightly compact, spherical shaped structure of PB-I .
Immunofluorescence light microscopy confirmed the spatial distribution of these prolamins within the PBs. CysR10 was visualized as small particles when labeled by anti-CysR10 followed by rhodamine-conjugated secondary antibodies (Fig. 1D). The distribution of CysR10 co-localized with CysP13, which was visualized with fluorescein isothiocyanate (FITC)-conjugated secondary antibodies (Fig. 1 E, F arrows). CysR10 was observed at the center of the PBs, whereas the distribution of CysP13 was more varied. Details about the spatial relationship between the prolamins were confirmed by immunofluorescence microscopy images from developing endosperm at 3 WAF (Fig. 2). They show that PB-I is composed of a center core of CysR10, surrounded by a middle layer of a mixture of CysR10 and CysP13, and then followed by a peripheral layer containing CysP13 devoid of CysR10. By immunoelectron microscopy, a more detailed structure of PB-I can be analyzed through its ultrastructure during different stages of seed development (at 5 DAF, 1 WAF, 2 WAF, and 3 WAF), then the Schematic images of PB-I structure during rice endosperm development can be obtained (Fig. 5).
The prolamin-containing PB-Is were non-spherical in the CysR10-repressed endosperm, because CysR10 is required for forming PB-Is into the spherical shape and for the compact size, and that it not only forms the central core but also interacts with other Cys-rich prolamins to assemble the concentric ring structure within the PB-I. In addition, RNAi suppression of CysR10 slightly reduced the expression level of CysP13, but CysR16 and CysR14 were normal or slightly higher amounts. However, Kawakatsu et al. reported that their 10 kDa prolamin-suppressed plant accumulated substantially higher levels (about three times compared with the wild type) of CysR14 (RM1 and RM9) and CysR16 (RP16) prolamins than normal, although CysP13 (RM2 and RM4) prolamins were lower amounts. This different result may due to the differences of the methods used to regulate down the CysR10 expression level . One is the conventional RNAi method with the inverted CysR10 open reading frame, and the other one is the expression of a modified human Glucagon-like peptide-1 (GLP-1) to regulate down the target proteins. This elevated levels of CysR14 and CysR16 may compensate for the loss of CysR10 and contribute to form a rigid normal sized PB-I. Another consist result came from an endosperm storage protein mutant that contains reduced levels of CysR16, CysR14 and CysR10 and displays abnormal large PBIs.
Protein disulfide isomerase (PDI) family oxidoreductase PDIL2;3 knockdown inhibited the accumulation of Cys-rich 10-kD prolamin (crP10) in the core of PB-I. Conversely, crP10 (CysR10) knockdown dispersed PDIL2;3 into the endoplasmic reticulum lumen .
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Labs working on this gene
1 Institute of Genetic Resources, Faculty of Agriculture, Kyushu University, Japan
2 Organization for General Education, Yamaguchi Prefectural University, Japan
3 Division of Plant Sciences, National Institute of Agrobiological Sciences, Tsukuba, Japan
4 Institute of Biological Chemistry, Washington State University, USA
5 Faculty of Life Science, Yamaguchi Prefectural University, Japan
- ↑ Pai-Hsiang Su; Su-May Yu; Ching-San Chen. Expression analyses of a rice 10 kDa sulfur-rich prolamin gene. Botanical Bulletin of Academia Sinica, 2004, 45(2): 101-109.
- ↑ 2.0 2.1 2.2 2.3 2.4 Ai Nagamine; Hiroaki Matsusaka; Tomokazu Ushijima; Yasushi Kawagoe; Masahiro Ogawa; Thomas W. Okita; Toshihiro Kumamaru. A Role for the Cysteine-Rich 10 kDa Prolamin in Protein Body I Formation in Rice Plant and Cell Physiology, 2011, 52(6): 1003-1016.
- ↑ 3.0 3.1 Yayoi Onda; Ai Nagamine; Mutsumi Sakurai; Toshihiro Kumamaru; Masahiro Ogawa; Yasushi Kawagoe. Distinct Roles of Protein Disulfide Isomerase and P5 Sulfhydryl Oxidoreductases in Multiple Pathways for Oxidation of Structurally Diverse Storage Proteins in Rice The Plant Cell, 2011, 23(1): 210-223.
- ↑ Ogawa, M., Kumamaru, T., Satoh, H., Iwata, N., Omura, T., Kasai, Z. et al. (1987) Purification of protein body-I of rice seed and its polypeptide composition. Plant Cell Physiol.28: 1517–1527.
- ↑ Masumura, T., Shibata, D., Hibino, T., Kato, T., Kawabe, K., Takeba, G. et al. (1989) cDNA cloning of an mRNA encoding a sulfur-rich 10 kDa prolamin polypeptide in rice seeds. Plant Mol. Biol. 12:123–130.
- ↑ Kawakatsu, T., Hirose, S., Yasuda, H. and Takaiwa, F. (2010) Reducing rice seed storage protein accumulation leads to changes in nutrient quality and storage organelle formation. Plant Physiol. 154: 1842–1854.
- ↑ Onda, Y., Kumamaru, T. and Kawagoe, Y. (2009) ER membrane localized oxidoreductase Ero1 is required for disulfide bond formation in the rice endosperm. Proc. Natl Acad. Sci. USA 106: 14156–14161.